buffer: Keep the shorter language setting names for the common operation (#43915)

cc
https://github.com/zed-industries/zed/pull/43888#issuecomment-3597265087

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/assistant_text_thread/src/text_thread.rs

@@ -1223,9 +1223,8 @@ impl TextThread {
         cx.spawn(async move |this, cx| {
             let markdown = markdown.await?;
             this.update(cx, |this, cx| {
-                this.buffer.update(cx, |buffer, cx| {
-                    buffer.set_language_immediate(Some(markdown), cx)
-                });
+                this.buffer
+                    .update(cx, |buffer, cx| buffer.set_language(Some(markdown), cx));
             })
         })
         .detach_and_log_err(cx);